Periodic Trends in Properties of Elements

3.7 Periodic Trends in Properties of Elements

The periodic table is not just a catalogue of elements — it is a map of repeating patterns. As you move down a group or across a period, physical and chemical properties change in predictable ways. For instance, within a period, chemical reactivity is high in Group 1 metals, low near the middle, and high again in Group 17 non-metals. Down a group of representative metals like the alkali metals, reactivity increases; down a group of non-metals like the halogens, reactivity decreases. These trends are not accidental — they arise from the structure of the atom itself: the number of electrons, the energy levels they occupy, and the pull of the nucleus.

We will examine five key physical properties that show clear periodic trends: atomic radius, ionic radius, ionization enthalpy, electron gain enthalpy, and electronegativity. For each, we will see the pattern, understand why it happens, and connect it to the underlying atomic theory.

--- …